- added link/unlink/link_fd fast_ops callbacks
- moved code from snd_pcm_link to pcm_hw.c
- moved "empty" routines pointing to slave to pcm_generic.c
- introduced snd_pcm_generic_t
The preamble values can be defined in iec958 plugin configuration.
As default, Z/Y/X=8/4/2 is used. CMI8338 has different values,
so override in its configuration.